Custom attributes (again)

[Manu]

On 6 April 2012 15:58, Steven Schveighoffer <schveiguy at yahoo.com> wrote:

> On Fri, 06 Apr 2012 03:54:15 -0400, Walter Bright <
> newshound2 at digitalmars.com> wrote:
>
>  On 4/6/2012 12:49 AM, Alex Rønne Petersen wrote:
>>
>>> What about type declarations? I think those ought to be supported too.
>>> E.g. it
>>> makes sense to mark an entire type as @attr(serializable) (or the
>>> inverse).
>>>
>>
>>
>> That would make it a "type constructor", not a storage class, which we
>> talked about earlier in the thread. I refer you to that discussion.
>>
>
> I think there is a huge misunderstanding here.
>
> A type constructor alters a type.  Annotations are not type constructors.
>
> for example:
>
> class C {}
>
> @foo class D {}
>
> @foo C c;
> @foo2 D d;
> D d2 = d;
>
> In all these cases, the @foo or @foo2 affects the *declaration*, not the
> *type*.  So:
>
> 1. D's type is not affected, it's still class D.  But an annotation has
> been stored on the *symbol* D, such that it can be looked up later.
> 2. annotations on variables do *not* affect the type of the variable.  The
> assignment to d2 works fine.
> 3. The following symbols have annotations attached to them:
>  C: none
>  D: @foo
>  c: @foo
>  d: @foo2
>  d2: none
>
> Note that d and d2 have no annotations attached even though they are of
> type D.  Because the type isn't affected by annotations.
>

Just to clarify, typeof(d) and typeof(d2) (ie, both D's) are still
annotated with foo, right? This is precisely how I imagine it to be.

An annotation is simply metadata, stored in the compiler, and looked up via
> compiler directives.  Optionally (and I would encourage this), TypeInfo
> would store annotations on type declarations for retrieval at runtime.
>

I agree, and I would also encourage this.
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